Clamping fixture for axially clamping a tool in place, in particular a disc

ABSTRACT

A clamping device for portable grinding machines comprising a clamping nut which can be screwed on to the end-side threaded step (13) of the drive spindle (10) to clamp a grinding disk (15) in place. The clamping nut carries a clamping fork (22) which, with its fork leg ends (26, 27), is held so as to be movable about a diametral pivot axis (30) between a clamping position and a loosened position. The ends (26, 27) are provided with eccentric pressing surfaces (28, 29) which decrease with regard to the eccentricity during the pivoting from the clamping position to the release position and act axially on the grinding disk (15) via a pressing disk (36). For releasing, the clamping fork (22) is pivoted about the pivot axis, surface areas of decreasing eccentricity of the pressing surfaces (28, 29) becoming effective. In the process, the thread (14, 20) is relieved and the clamping nut loosened, which can be fully unscrewed manually by taking hold of the clamping fork (22). This enables a grinding disk to be changed quickly and safely without a tool (FIG. 1).

BACKGROUND OF THE INVENTION

My invention relates to a clamping device or chuck for axially clampinga tool and, more particularly, to a clamping device for a tool used in aportable powered hand tool, e.g. for a grinding disk in a portablegrinding machine.

My invention is based on a chuck for axially clamping a tool, especiallya disk-shaped tool or tool disk, on a flange of a driven spindlecomprising a clamping nut which is provided with an internal thread andwhich can be screwed onto an end-side threaded step of the spindle, anda clamping member which is positioned axially between the tool on oneside and the clamping nut on the other side and can press the toolagainst the flange. A clamping fixture of the said type has beendisclosed (German Patent Specification No. 3,012,836) in which theclamping member consists of an element which is roughly hat-shaped incross-section and is axially supported against the flange of theclamping nut via a helical spring. When the clamping nut is screwed onand tightened, the hat-shaped clamping element is pressed axiallyagainst the tool via the axially compressed spring, and the tool isthereby tightened against the flange on the spindle side, the end faceof a cylindrical extension of the clamping nut coming to bear directlyon a facing axial side of the flange on the spindle side and, duringfurther tightening of the clamping nut, the flange on the spindle sidebeing tightened together with the clamping nut. This is to ensure in anangle grinder that the grinding disc is mounted with a definite contactpressure and that this contact pressure remains at the right level. Thisclamping device is also intended to permit a quick and simplereplacement of the grinding disk and at the same time avoid overloadingof the powered hand tool, in particular the angle grinder. This isbecause, if the torque acting on the grinding disk is too great, thegrinding disc stops, while the flange and also the clamping nut havingthe clamping member perform a relative movement thereto. The effect ofthe clamping nut automatically tightening further in operation, whichotherwise makes it considerably more difficult to loosen the clampingnut when changing the grinding disk, is counteracted with this clampingfixture. Nonetheless, loosening of the clamping nut is here onlypossible with the assistance of a special auxiliary tool. The spindle,depending on the design of the machine, must be appropriatelycounterheld by a second auxiliary tool, e.g. a spanner.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aclamping device for axially clamping a tool, especially a grinding disk,in which a tool change can be made without an aixiliary tool such as aspanner. Another object is to be able to easily modify existing powertools.

In keeping with these objects and with others which will become apparenthereinafter, the clamping member is held on the clamping nut so as to bemovable relative to the clamping nut between a clamping position and aloosened position and has at least one pressing surface dropping axiallyin a direction of motion from the clamping position to the loosenedposition.

In the clamping device according to the invention having thecharacterizing features of the main claim, the following advantagesresult. A tool change is made possible without any auxiliary tool. Thistool change, in addition, can be performed quickly and safely. A furtheradvantage is that powered hand tools already existing can also bechanged over without special redesign. For example, a simple exchange ofthe clamping nut is sufficient for this purpose. Since, when theclamping member is transferred from the clamping position into therelease position, the axial clamping force of the clamping fixture isreduced and removed to such an extent that axial force no longer acts onthe thread, the spindle, in the release position, when the clamping nutis unscrewed further by hand, is no longer loaded by a torque. Only thethread friction of the relieved thread has to be overcome. Therefore aspecial spindle-locking device, as is otherwise present in certainpowered hand tools, is not required on the machine side. Where there isno spindle-locking device, it is not necessary, when unscrewing theclamping nut, for the spindle to be counterheld with an additionalauxiliary tool, e.g. a spanner. In spite of that, the clamping nut canas before be designed conventionally, e.g. as standard, so that it isstill possible in especially stubborn cases, e.g. in the event of arusted-in clamping nut, for a spanner to be placed thereon and for theclamping nut to be released with this auxiliary tool.

Advantageous further developments and improvements of the clampingfixture specified in the main claim are possible by the features recitedin the subclaims.

There are several advantageous embodiments of my invention. The clampingmember can be held on the clamping nut so as to be pivotable about adiametral pivot axis and has at least one pressing surface which iseccentric with regard to this pivot axis and whose radial distance fromthe pivot axis decreases in the pivoting direction. An intermediatemember, e.g. a pressure disk, to transmit pressure more uniformly can bearranged between the pressing surfaces and the tool. The clamping toolmay be in the form of a clamping fork with two fork legs having fork legends which partially rest in recesses in the clamping nut and which ispivotably mounted in the clamping nut. Each fork leg end can have aneccentric pressing surface which acts directly or indirectly via thepressing disk on the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is described in greater detailbelow and is shown in the drawing, in which:

FIG. 1 is a schematic, axial longitudinal cross sectional view of aclamping device as part of an angle grinder having a mounted grindingdisk,

FIG. 2 is a schematic perspective view merely of the clamping nut of theclamping device,

FIG. 3 is a schematic perspective view merely of the clamping member,

FIG. 4 is a schematic bottom view of the clamping nut in arrow directionIV in FIG. 2.

FIG. 5 is a schematic perspective view of another embodiment of aclamping member according to our invention.

FIG. 6 is a schematic, axial longitudinal section through anotherembodiment of a clamping device according to our invention.

FIG. 7 is a schematic perspective view of an additional embodiment of aclamping member according to out invention.

FIG. 8 is a schematic axial cross sectional view through the embodimentshown in FIG. 1 with the clamping member in a loosened state.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows the lower part of a portable powered handtool which is designed, for example, as an angle grinder and has aspindle 10 which is motor-driven via a gearing and, at the end, mergesvia an annular shoulder 11 into a cylindrical step 12 of smallerdiameter and then into an end-side threaded step 13 having an externalthread 14. The spindle 10 serves to drive a tool 15 which consists, forexample, of the grinding disk indicated or another tool disc, a rubberplate or the like. The tool 15 is mounted and clamped in place between aflange 16 and a clamping nut 17. The flange 16 is axially supported onthe annular shoulder 11 and centered radially on the cylindrical step12. It is coupled in a positive-locking manner to the spindle 10.

The clamping nut 17 has a flange 18 and a cylindrical sleeve part 19protruding therefrom and is provided with a through-going internalthread 20 with which the clamping nut 17 is screwed onto the externalthread 14 of the threaded step 13. The tool 15 is centered on the outerperipheral surface of the cylindrical sleeve part 19 during mounting.

Arranged in the axial area between the tool 15 on the one side and theclamping nut 17 on the other side is a clamping member 21 which hereconsists of a clamping fork 22. In the exemplary embodiment shown (FIG.3), the clamping fork 22 has two fork legs 23, 24, each of which iscurved and which together form a roughly semicircular curved part fromwhich a manipulating nose 25 protrudes. Of the two fork legs 23, 24,only their ends 26 and 27 respectively can be seen in FIG. 1. Thisclamping member 21 can be acted upon by the clamping nut 17 by anaxially directed pressing force and is able to press axially against thetool 15 and press the latter against the axial end face of the flange16.

The clamping member 21 in the form of the special clamping fork 22 isheld so as to be movable relative to the clamping nut 17 between aclamping position shown in FIG. 1 and a release position or in aloosened state shown in FIG. 8. For each end 26, 27 of the fork leg 23,24, it has an axially directed pressing surface 28 and 29 which drops ina direction of movement from the clamping position (FIG. 1) to therelease position (FIG. 8).

In the exemplary embodiment shown, the clamping member 21 in the form ofthe clamping fork 22 is held so as to be pivotably movable on theclamping nut 17 about a preferably diametral pivot axis 30 by means ofbearing pins 31 and 32 respectively. The respective pressing surface 28or 29 is eccentric with regard to the pivot axis 30. If the clampingfork 22 is located in its clamping position according to FIG. 1, whichroughly corresponds to the horizontal pivot position according to FIG.3, the part of the pressing surface 28 or 29 having the greatesteccentricity e max, with regard to the pivot axis 30, is effective. If,on the other hand, the clamping fork 22, with regard to FIG. 1, ispivoted downwards and in arrow direction 33 about the pivot axis 30 intothe release position, the part of greatest eccentricity of the pressingsurface 28, 29 is moved away and the part of the pressing surface 28, 29which has an eccentricity decreasing with increasing pivot angle down tothe minimum eccentricity e min comes into function.

The respective pressing surface 28, 29, roughly in the surface area ofgreatest eccentricity e max, has a surface portion 34 and 35 (FIG. 3),or instead a surface portion having an eccentricity already reducedagain. This ensures that, when clamping fork 22 is located in theclamping position according to FIGS. 1 and 3, it is in a stable clampingposition around the pivot axis 30.

In principle, the clamping nut 17 with the pressing surface 28, 29 ofthe clamping fork 22 can axially act directly upon the tool 15. A betterpressure distribution in the peripheral direction is achieved when anintermediate member in the form of a pressure disk 36 is also arrangedbetween the tool 15 and the pressing surface 28, 29, this pressure disk36 is in turn acted upon by the eccentric pressing surface 28, 29 andpresses axially with an end face against the tool 15. The pressure disk36 is likewise centered on the cylindrical sleeve part 19 of theclamping nut 17 and guided in an axially movable manner.

As is apparent from FIG. 1, each end 26, 27 of the fork legs 23 and 24respectively, with the eccentric pressing surface 28 and 29respectively, protrudes in the axial direction beyond the end face 37,pointing towards the tool 15, of the flange 18 of the clamping nut 17 sothat the clamping nut 17, solely with this pressing surface 28, 29,exerts axial pressing force on the tool 15 via the pressure disk 36.Contained in the flange 18 are apertures 38 and 39 which are locateddiametrically opposite one another along the pivot axis 30 and in whichat least the ends 26 and 27 of the fork legs 23 and 24 respectively areaccommodated. Provided the ends 26, 27 of each fork leg 23 and 24respectively are offset by an appropriate distance from the latter, theclamping fork 22, in the clamping position according to FIGS. 1, 3, canrest on the end face 40, pointing downwards in FIG. 1, of the clampingnut 17 and can protrude downwards beyond this end face 40 provided thisdoes not cause further obstruction. Another advantageous design followsfrom FIGS. 2 and 4. Contained here in the end face 40 of the clampingnut 17 are recesses 41, 42 which are dimensioned to be so wide and deepthat, when clamping fork 22 is located in clamping position, its twocurved fork legs 23, 24 find space in the recess 41 and its manipulatingnose 25 finds space in the recess 42 so that the clamping fork 22 doesnot protrude axially beyond the lower end face 40 of the clamping nut17.

FIG. 1 shows the clamping device in the clamping position in which thetool 15, via the clamping nut 17 plus clamping fork 22 and via thepressure disk 36, is clamped axially in place on the flange 16.

If the tool 15 is to be removed and changed, first of all, by takinghold of the manipulating nose 25, the clamping fork 22 is pivoteddownwards in arrow direction 33 about the pivot axis 30 in FIGS. 1 and3. In the process, the pressing surface 28, 29 slides along on theallocated end face of the pressure disc 36, the surface area of greatesteccentricity e max being pivoted away and a surface area which has aneccentricity decreasing as a function of the pivot angle down to e minmoving into this region. The result of this is that the internal thread20 and external thread 14 are relieved and thus the axial clamping forceacting on the tool 15 from the clamping nut 17 is reduced to such anextent that hereafter the clamping nut 17 can be completely unscrewedfrom the threaded step 13 by hand. In the process, the clamping member21 now pivoted into release position can facilitate the unscrewingmovement by being grasped for unscrewing.

If the tool 15 has been exchanged and a new one is to be mounted andclamped, the procedure is as follows. First the flange 16 is slippedonto the spindle 10. After this, the new tool 15, together with thepressure disk 36, is located in position and then the clamping nut 17 isplaced on and screwed onto the threaded step 13. In the process, itscylindrical sleeve part 19 passes through the tool 15 and the pressuredisk 36, which is centered thereon. When the clamping nut 17 is beingscrewed on, the clamping fork 22 is swung into its clamping positionaccording to FIGS. 1, 3 in which it is held firmly on account of theflat portions 34, 35. During work with the hand tool, i.e. when themotor is switched on and the spindle 10 is driven rotationally, theclamping nut 17, as usual, tightens further automatically.

The clamping device described is exceptionally simple, cost-effectiveand quick, safe and easy to handle. It enables the tool 15 to be quicklyand safely changed without requiring additional special tools for thispurpose. A further advantage is that existing powered hand tools, inparticular grinding machines, can also be subsequently equipped withthis clamping device without further redesign. For this purpose, onlythe clamping nut, in general, needs to be replaced by the clamping nut17 according to the invention having pressure disk 36. Furthermore, itis advantageous that, when the clamping fork 22 is being transferredfrom the clamping position according to FIG. 1 into the releaseposition, no torque is exerted on the spindle 10 so that powered handtools equipped with such a clamping device no longer require anintegrated spindle-locking device. This is because, to unscrew theclamping nut 17, after the transfer into the release position, only thethread friction of the relieved thread 14, 20 has to be overcome andtherefore a very small moment has to be applied. For this purpose, thefriction on the machine side from the spindle 10 up to the drive motoris sufficient as a brace for the spindle 10.

In addition, the clamping nut 17 is designed in such a way that, asbefore, it also enables, if necessary, a special tool to be applied,e.g. in the form of a pin-type face spanner, so that in particularlystubborn cases, e.g. in the slightly rusted state, the clamping nut 17can also be loosened in a conventional manner by means of an auxiliarytool.

The clamping fixture described is suitable for clamping all possibletools 15 and in connection with various types of powered hand tool. Itis especially suitable for grinding machines, e.g. angle grinders, andhere for clamping disk-shaped tools 15 in place.

In another exemplary embodiment shown in FIG. 5, instead of the slidingfriction, rolling friction is present between the clamping member 21,exerting the axial clamping force, and the tool 15 or the pressure disk36. Thus the pressing surface 28, 29 is, for example, in each caseprovided on a rolling element 5 of the clamping member. The rollingelement 5 can, for example, consist of an eccentric roller 56.

In this embodiment there are two rolling elements 55 mounted on axles 51which engage in clamping nut 17.

In another exemplary embodiment as shown in FIG. 6, the clamping member21 is configured as clamping fork 22 according to the first exemplaryembodiment. In this arrangement, an intermediate member permittingrolling friction is located between the pressing surface 28, 29 on theone side and the pressure disk 36 or the tool 15 directly on the otherside, which intermediate member, for example, has a plurality of rollers53, e.g. needle bodies, which, during the movement of the clampingmember 21, are acted upon by the pressing surface 28, 29 and permitrolling friction instead of the sliding friction. In this way, thestability is increased and, furthermore, the clamping fork 22 can bepivoted from the clamping position into the release position in anespecially easy-running manner.

In another exemplary embodiment (not shown), the clamping member is heldso as to be rotationally movable relative to the clamping nut 17 about arotational axis R coaxial to the clamping nut 17. In this arrangement,it has a sloping surface S which, with regard to a flat axial surface ofthe clamping nut 17, rises in one direction and whose axial distancefrom the flat axial surface decreases in the rotational direction fromthe clamping position to the loosened position.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofstructures differing from the types described above.

While the invention has been illustrated and described as a clampingdevice or chuck for axially clamping a tool, especially a tool disk, itis not intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:
 1. A clamping device for axially clamping a tool, inparticular, a disk tool on a flange of a rotatable spindle having anend-side threaded step, said clamping device comprising a clamping nuthaving an inner thread cooperating with the end-side threaded step ofthe spindle for securing the tool on the spindle; and a clamping memberaxially positioned between the tool and said nut, said clamping memberbeing supported on said clamping nut for pivotal movement relativethereto about a substantially diametral axis and having pressure surfacemeans for applying a clamping force to the tool, said pressure surfacemeans comprising at least one pressure surface arranged eccentricallyrelative to said substantially diametral axis,an axially moveablepressure disk positioned between the tool and said clamping member, saidclamping member comprising a clamping fork having two fork legs withfork leg ends, said two fork leg ends are pivotally mounted on saidclamping nut about the diametral axis, each of said fork leg ends havingan eccentric pressing surface which protrudes axially beyond a clampingnut end face and acts via said pressure disk upon the tool, wherein saidclamping nut is provided with a plurality of recesses, and said clampingfork with said fork legs is at least partially accommodated in saidrecesses in the clamping position.
 2. A clamping device according toclaim 1, wherein said clamping member is pivotably movable betweenclamping and release positions, a radial distance of said one pressuresurface from said substantially diametral axis decreasing in a directionof a pivotal movement of said clamping member from the clamping positionto the release position.
 3. A clamping device according to claim 1,wherein said said clamping member includes a rolling element definingsaid pressure surface means.
 4. A clamping device according to claim 3,wherein said rolling element comprises an eccentric roller.
 5. Aclamping device according to claim 1, wherein said pressure diskcomprises a plurality of rollers which during movement of said clampingmember, roll on said at least one pressing surface.
 6. A clamping deviceaccording to claim 1, wherein said eccentric pressing surface has a flatarea located substantially in an area of maximum eccentricity.
 7. Aclamping device according to claim 1, wherein said clamping fork withsaid fork legs partially rests in the clamping position on said clampingnut end face adjacent the tool and partially protrudes beyond a portionof said end face.
 8. A clamping device for axially clamping a tool, inparticular, a disk tool on a flange of a rotatable spindle having anend-side threaded step, said clamping device comprising a clamping nuthaving an inner thread cooperating the end-side threaded step of thespindle for securing the tool on the spindle; and a clamping memberaxially positioned between the tool and said nut, said clamping memberbeing supported on said clamping nut for pivotal movement relativethereto about a substantially diametral axis and having pressure surfacemeans for applying a clamping force to the tool, said pressure surfacemeans comprising at least one pressure surface arranged eccentricallyrelative to said substantially diametral axis,an axially moveablepressure disk positioned between the tool and said clamping member, saidclamping member comprising a clamping fork having two fork legs withfork leg ends, said fork leg ends are pivotally mounted on said clampingnut about the diametral axis, each of said fork leg ends having aneccentric pressing surface which protrudes axially beyond a clamping nutend face and acts via said pressure disk upon the tool, wherein saidclamping nut has a flange provided with apertures and said fork leg endsare accommodated in said apertures.